1. Field of the Invention
The present invention relates to a sewing machine, and more particularly, it relates to a sewing machine having a balance.
2. Description of the Prior Art
A sewing machine having a balance is known in general. This balance has a thread engaging part. The balance is so structured that the thread engaging part captures and pulls a needle thread when forwardly moving from left to right. In this case, the thread engaging part of the balance engages with the needle thread passing through thread receiving openings of a pair of thread guide plates for pulling the same.
When a sewing machine operating switch of the conventional sewing machine having the aforementioned structure is moved to OFF for stopping the sewing machine, however, a motor is generally stopped when a needle is located on a top dead center. When the needle is located on the top dead center, the thread engaging part of the balance is generally located on an intermediate position of the passage for the forward movement beyond the thread guide plates. In other words, the motor is generally stopped regardless of the position of the thread engaging part of the balance.
Therefore, when the sewing machine operating switch is moved to ON after the needle thread is exchanged, for example, the sewing machine starts the first operating cycle without capturing and pulling the needle thread by the thread engaging part of the balance. Thus, the needle thread has no prescribed slack in the first operating cycle of the sewing machine and hence a slack portion formed on a lower portion of cloth for engaging with the forward end of a shuttle body disappears following an operation of a thread take-up spring pulling up the needle thread when the needle passes through the cloth. This may disadvantageously result in formation of no first stitch (the so-called skipping stitch).
When the sewing machine operating switch is moved to ON without exchanging the needle thread, the needle thread may be in a state disengaging from the thread engaging part of the balance due to slacking during the unused state of the sewing machine. In this case, inconvenience similar to the above takes place to disadvantageously result in the so-called skipping stitch.
An object of the present invention is to provide a sewing machine capable of preventing formation of no first stitch (the so-called skipping stitch), which is readily caused immediately after the sewing machine starts to operate.
Another object of the present invention is to automatically move a balance in the aforementioned sewing machine.
A sewing machine according to an aspect of the present invention comprises a thread guide plate having a thread receiving opening, a balance having a thread engaging part and reciprocating through the thread guide plate so that the thread engaging part captures and pulls a needle thread when forwardly moving from left to right, a first detector detecting that the thread engaging part of the balance is located in the vicinity of a forward movement starting point leftward beyond the thread receiving opening of the thread guide plate and an indicator operating on the basis of a detection signal received from the first detector.
The sewing machine according to this aspect is provided with the first detector detecting that the thread engaging part of the balance is located in the vicinity of the forward movement starting point leftward beyond the thread receiving opening of the thread guide plate and the indicator operating on the basis of the detection signal received from the first detector as described above, whereby the operator can recognize that the thread engaging part of the balance is located in the vicinity of the forward movement starting point leftward beyond the thread receiving opening of the thread guide plate through the indicator. When the operator moves the balance to a position for turning on the indicator, guides the needle thread and thereafter operates the sewing machine, therefore, the thread engaging part of the balance can reliably capture and pull the needle thread also immediately after the sewing machine starts to operate. Consequently, formation of no first stitch (skipping stitch), which is readily caused immediately after the sewing machine starts to operate, can be prevented.
The sewing machine according to the aforementioned aspect preferably further comprises an upper shaft so rotating that the balance reciprocates in association with rotation thereof, a motor driving the upper shaft and a thread guide mode switch driving the motor. According to this structure, the balance can be automatically moved with the thread guide mode switch, whereby operability in thread guiding can be improved. In this case, the motor is preferably stopped on the basis of the detection signal from the first detector after the thread guide mode switch is moved to ON. According to this structure, the thread engaging part of the balance can be automatically moved to the position in the vicinity of the forward movement starting point leftward beyond the thread receiving opening of the thread guide plate.
In the structure of the sewing machine comprising the upper shaft, the first detector preferably includes a first detected element provided on the upper shaft and a first photoelectric switch detecting the first detected element. In this case, the first photoelectric switch of the first detector preferably detects the first detected element when the thread engaging part of the balance is located in the vicinity of the forward movement starting point leftward beyond the thread receiving opening of the thread guide plate. According to this structure, the first detector can readily detect that the thread engaging part of the balance is located in the vicinity of the forward movement starting point leftward beyond the thread receiving opening of the thread guide plate.
The sewing machine according to the aforementioned aspect preferably further comprises a sewing machine operating switch operating the sewing machine, and the indicator is preferably responsively inactivated when the sewing machine operating switch is moved to ON. According to this structure, the indicator can be prevented from operating during operation of the sewing machine. In this case, the motor is preferably stopped to stop a needle on a top dead center when the sewing machine operating switch is moved to OFF.
The sewing machine according to the aforementioned aspect preferably further comprises a sewing machine operating switch operating the sewing machine, the indicator preferably includes an LED, and the LED is preferably turned on when receiving the detection signal from the first detector while the motor is stopped and turned off when the sewing machine operating switch is moved to ON. According to this structure, the operator can readily recognize that the thread engaging part of the balance is located in the vicinity of the forward movement starting point leftward beyond the thread receiving opening of the thread guide plate when the LED is turned on.
The sewing machine comprising the aforementioned upper shaft preferably further comprises a second detector for detecting at least the rotational position of the upper shaft, and the motor is preferably stopped on the basis of a detection signal received from the second detector. According to this structure, the motor can be readily stopped when the upper shaft reaches a prescribed rotational position, for example. Thus, the motor can be stopped on a prescribed position such as the top dead center of the needle by controlling the relation between the rotational position of the upper shaft and the position of the needle. In this case, the second detector includes a second detected element provided on the upper shaft and a second photoelectric switch detecting the second detected element. According to this structure, the rotational position of the upper shaft can be readily detected.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.